1. Technical Field
The present invention relates to a semiconductor laser element having a window region and a current confinement structure and a method of manufacturing the semiconductor laser element. The contents of the following Japanese patent application are incorporated herein by reference,
No. 2010-101281 filed on Apr. 26, 2010
2. Related Art
When optical output from a semiconductor laser element is increased, heat may be generated near the facet due to light absorption. In this case, the heat could melt the facet so that the function of the laser element is terminated, possibly resulting in a phenomenon called COD (Catastrophic Optical Damage), which causes a problem of degrading the reliability of the semiconductor laser element. Techniques being developed to solve this problem involve making the facet transparent. By making the facet transparent, the optical output limit before the COD occurs can be improved.
Making the facet transparent involves widening the energy band gap of the semiconductor region near the facet of the semiconductor laser element, thereby causing the region near the facet to be transparent with respect to the emission wavelength and eventually preventing the light absorption. This transparent region is referred to as a “window region”. The region that is surrounded by the window region, which is not transparent with respect to the light of interest, is referred to as a “non-window region”. One specific method known for making the facet transparent involves disordering a semiconductor region near the facet by diffusing impurities or vacancies in the semiconductor region, thereby widening the energy band gap (see, for example, Patent Documents 1 to 4).
In order to inject current with high density into the active layer of the semiconductor laser element, the semiconductor laser element adopts a current confinement structure. The current confinement structure is a structure in which an n-type semiconductor current confinement layer is buried in a p-type semiconductor layer with an opening region of a predetermined width, for example. In the current confinement structure, the hole carriers injected from the upper portion of the p-type semiconductor layer flow only through the opening region of the current confinement layer. By decreasing the width of the current path, the current is injected to the active layer with increased current density. As a result, it is possible to achieve more efficient current injection and laser oscillation (see, for example, Patent Documents 1 and 2). The width of the region serving as the current path in the current confinement structure is referred to as the current confinement width.
Patent Document 1: Japanese Patent Application Laid-open No. 2007-242718
Patent Document 2: Japanese Patent Application Laid-open No. H09-23037
Patent Document 3: Japanese Patent Application Laid-open No. H10-200190
Patent Document 4: Japanese Patent Application Laid-open No. 2001-15859